There are numerous requirements for sealing the annulus between two stationary concentric rigid members, with such applications usually requiring that the seal be effective against large fluid pressures. One such requirement which is increasingly difficult to satisfy is for sealing between concentric well members, as between a wellhead member and a casing string or between a wellhead member and one or more tubing strings, particularly when the seal is to be established by remote operations at considerable depth under water in an offshore well installation.
Historically, such seals have been established by elastomeric sealing elements, as seen for example in U.S. Pat. No. 3,268,241 to Castor et al, or by using so-called metal lip seals, as in U.S. Pat. No. 3,378,269 to Castor, or by using Laurent seals of the type shown for example in U.S. Pat. No. 2,687,229 to Laurent. The conditions under which such seals must operate have become increasingly severe, particularly in offshore well applications. Thus, specifications for offshore well installations now frequently require that such seals be effective against internal pressures at the wellhead of 15,000 p.s.i., and that capability frequently must be achieved under conditions of remote installation of the two concentric members and of the seal device itself. Particularly in the offshore well industry, there has been a trend away from elastomeric sealing elements toward metal-to-metal seals, with the metal-to-metal seal being viewed as a more dependable device over a long time period than seals depending upon elastomeric materials. However, conventional metal-to-metal sealing elements, such as the metal lip seals, depend upon elastic deformation of the sealing element, first mechanically and then in response to the pressure against which the seal is to act, and such devices have not always been dependably successful. Further, such devices must have a shape allowing the seal device to be elastically deformed under mechanical pressure applied by the parts being sealed, and this requirement has in some cases resulted in damage to the seal element, or the surfaces against which that element is to act, during remote installation of the seal element. There has thus been a continuing need for improvement, particularly when a metal-to-metal sealing action is needed.